1. Field of the Invention
This invention relates generally to squeeze cementing of oil or gas wells and, more specifically to a latching device between tubing and the squeeze packer assembly used for cementing an oil or gas well.
2. Description of the Related Art
Cementing is the term used for the process of placing a slurry, usually formed by combining a cementitious material with a liquid, into the annulus between the outside of the casing in the hole and the wall of the hole. Placement of cement is usually done by pumping. Squeeze cementing is the most common type of remedial (secondary) cementing. The process involves applying hydraulic pressure to force or squeeze a cement slurry in contact with a formation, either in open hole or through perforations in the casing or liner.
In many conditions a cement slurry may be applied to water, oil or gas bearing portions of a producing zone to eliminate excessive water or gas without sealing off the oil. This process is especially beneficial in correcting producing well defects. In addition, squeeze cementing may be used when an oil-producing zone is to be isolated from an adjacent gas zone, and the gas/oil ratio can usually be improved to help increase oil production. Additionally, water sands can be squeezed off below the oil sand to help improve water/oil ratios. Independent water zones can be squeezed to eliminate water intrusion. Further, a casing leak may be repaired by squeezing cement through the leak.
Additional applications of squeeze cementing include sealing low pressure zones that imbibe oil, gas or drilling fluids, overcoming channeling or insufficient annular fillup behind the casing, and protecting against fluid migration into a producing zone. Additionally, squeeze cementing is sometimes employed to seal off perforations or plug a depleted open hole producing zone. This helps prevent fluid migration to and from the abandoned zone.
The most effective methods of squeeze cementing, and the most widely applicable, are the packer method and the hesitation squeeze method. In the packer method, the interval to be squeezed is isolated from the surface by a packer run and set on tubing. Many types of packers are available, each designed for specific well conditions. Either retrievable or permanent (drillable) packers can be used. To isolate the section below the perforations to be squeezed, a drillable or retrievable bridge plug may be placed below the perforations. The upper perforations are then squeezed and the remaining slurry reversed out.
The hesitation method involves the placement of cement in a single stage, but divides the placement into alternate pumping/waiting periods. This hesitation practice utilizes controlled fluid loss properties of the slurry to build filter cake nodes against the formation and inside the perforations while the parent slurry remains in a fluid state in the casing.
Equipment commonly employed in squeeze cementing includes high pressure pumps, drillable type squeeze packers and bridge plugs, and retrievable type squeeze packers and bridge plugs. Bridge plugs provide a pressure and fluid boundary between sections of casing. Multiple zones can be isolated individually for the desired treating or testing procedures.
Squeeze packers are designed to provide pressure or fluid control for remedial cementing operations. The squeeze packer tool may be used in conjunction with the work string tubular. Typically, a valve built in the squeeze packer tool helps hold cement in place by providing downhole pressure control. In addition to this control feature, the squeeze packer tool may be designed to be removed from the well by the use of common oil well drilling equipment and practices.
An example of a squeeze packer assembly is the "EZ DRILL SV.RTM.", which is a drillable squeeze packer available from Halliburton in various tool and casing size configurations Squeeze Packer from Halliburton Services of Duncan, Okla. Fluid movement through the EZ DRILL SV.RTM. Squeeze Packer is controlled with a pressure balanced sliding valve which is operated by axial reciprocation of the tubing. The valve may be opened or closed, if desired, before and after squeeze cementing. Fluid movement through the valve will not affect the valve's position. When the valve is in the closed position, the packer is sealed against fluid or gas movement in either direction. When the valve is in the open position, fluid may be pumped through the packer or pressure may be relieved from below it. An unrestricted flow passage is provided through side ports in the packer tool.
The EZ DRILL SV.RTM. Squeeze Packer may be set on tubing (drill pipe), electrical wire line or sand line. The packer may be converted for use as a bridge plug (no fluid movement in either direction through the tool) before running in the hole.
Thus, a squeeze packer assembly may be inserted downhole and the stinger end of the tubular inserted to open and close the valve in the packer as desired. However, when the stinger is pulled from the packer to close the valve, there is a risk that the stinger may be pulled completely out of the packer. This is a serious problem because the axial displacement of the tubular at the top of the hole may not correspond to the axial displacement where the stinger connects with the squeeze packer valve. One of the problems resulting from pulling the stinger out of the squeeze packer is the risk of cement leaking out which potentially could cement the tubing in the hole.
Therefore, a device is needed to prevent inadvertently pulling the stinger end of the tubular completely out of the squeeze packer. Attempts have been made to design a snap-in/snap-out type latch that provides a surface indication of the stinger being landed in the squeeze packer, giving assurance that the sleeve valve is open, or the stinger being removed from the packer, indicating the sleeve valve is closed. Such devices are intended to provide the operator with a positive indication that the control valve of the packer is in the closed or open position while the stinger remains locked in the retainer of the packer during testing of the tubing. One example of such a device is the snap-latch stinger subs available from Baker Service Tools. However, such latches have the disadvantage that internal mechanisms were required in the squeeze packer itself. The latch mechanism required modification to provide engagement members (such as teeth) on the inside of the mandrel, or engagement members on the stinger assembly itself. These modifications were disadvantages because they could not be easily applied to existing equipment.